This project is aimed at determining what aspects of sensory information reach the cerebellum and what types of information processing are performed by the cerebellum. A rather special sensory system, the electrosensory system, present in a group of lower vertebrates (weakly electric fish) is invariably associated with an enlarged cerebellum. In preliminary studies I have shown that there is a functional connection between this sensory system and the cerebellum and that this particular cerebellar input is very amenable to physiological investigation. Specific questions that will be investigated during this project are: 1) What are the types and properties of cerebellar cells responding to adequate stimulation of the electrosensory system? 2) What are the major afferent and efferent pathways associated with this portion of the cerebellum? 3) What are the properties of cerebellar cells receiving multiple categories of sensory input? 4) How are the receptive fields of cerebellar cells organized and how do these compare with the receptive fields of cells in brain areas afferent to the cerebellum? 5) What is the acuity or discrimination ability of the electrosensory system at the level of the cerebellum and how does this compare with the acuity in areas afferent and efferent to the cerebellum? This will be an electrophysiological study; extracellular recordings of individual cell's activity will be the main type of data collected. Many types of stimuli will be used ranging from direct electrical activation of various brain areas for physiological mapping of the neural pathways to natural stimulation of the electrosensory system with stimuli designed to facilitate measurement of the descrimination ability of the system.